Conventionally, sewing machines executing embroidery sewing with attachable/detachable attachment of an embroidery frame drive unit thereto sews embroidery on a workpiece cloth based on sewing data for a pre-selected embroidery pattern by attaching an embroidery frame holding a workpiece cloth to be sewn on a carriage of the embroidery frame drive unit and moving the embroidery frame in the X-direction and the Y-direction. Thus, such sewing machines are provided with plurality types of embroidery frames such as rectangular, circular, and oval shapes varying in size and shape of the embroidery pattern for use in sewing embroidery.
Such being the case, sewing machines capable of embroidery sewing detect the type of embroidery frame attached to the carriage in order to check whether or not an embroidery frame having smaller embroidery area compared to the size of the intended embroidery pattern has been attached by mistake.
For example, the embroidery frame carrier unit disclosed in patent document 1 (JP 2002-52283 A page 5 to 7, FIGS. 10 and 14) is configured so that three detection switches are disposed in the carriage of the frame carrier unit in a single longitudinal row, while three switch activators corresponding to the three detection switches are provided in a connection portion of the embroidery frame so as to be associated with the three detection switches. When the connecting portion of the embroidery frame is slid into attachment with the carriage by sliding the embroidery frame from the front to the rear direction, the type of embroidery frame attached to the carriage is detected based on whether each of the three detection switches are activated or not depending upon the presence/absence of the switch activators.
Since the embroidery frame carrier unit described in patent document 1 is merely provided with three detection switches in the carriage, the combinations of ON signals and OFF signals delivered from the three detection switches only allow detection of maximum of eight types of embroidery frames. Moreover, dedicated switch activators for each type of embroidery frame must be disposed to each embroidery frame, thus disallowing the use of embroidery frames without switch activators. Furthermore, in addition to disposing plurality of detection switches to the carriage, and increased complexity in wiring interconnects for signal transmission that connect to each detection switches to the movable carriage, input ports for a CPU constituting a control unit need to be prepared as many as the number of detection switches, thereby leading to problems such as cost increase in the control unit.